The present invention relates to a wood splitter of the kind which includes a fixed splitting wedge and a hydraulically-driven pressure plate for advancing wood pieces towards and against the wedge.
Known hydraulic wood splitters of this kind normally comprise a double-acting hydraulic piston-cylinder device and a hydraulic feed circuit which operates at constant, high pressure. The high pressure hydraulic circuit is connected to different sides of the piston by means of a manually adjustable valve, such connection being made in dependence on whether the pressure plate is to carry out a working or return stroke. A hydraulic fluid tank is connected to the other side of the piston at the same time.
One drawback with these known arrangements is that the hydraulic pump must be driven continuously by a prime mover, in order to maintain a constantly high-feed pressure. In addition to unnecessary operating costs, this drawback necessitates the use of a large oil and tank volume in order to achieve requisite cooling of the oil, due to the fact that the oil is heated considerably during operation of the splitter. For example, with a hydraulic flow of 10-15 l/min., it is necessary to use a tank whose which volume corresponds to 2.5-3 times this flow rate. Another drawback is that adjustments to the setting of the high pressure valve in order to effect a working stroke or a return stroke of the pressure plate must be carried out by means of a manually actuable valve assembly, which because of the high oil pressure that prevails is relatively complicated. Because of these drawbacks of the known wood splitter of the aforesaid kind, the splitter has a very heavy and bulky construction and cannot therefore be transported easily between different working sites. For example, commercially available wood splitters of this kind may weigh from 100 to 150 kg.
The present invention is based on the realization that the aforesaid drawbacks are eliminated, among other things, when a single-acting piston-cylinder device is used instead of a double-acting device, so that the high feed pressure required need only be generated during a working stroke of the pressure plate. This greatly reduces the need to cool the oil, thereby also reducing the requisite tank volume. The pressure plate may be returned to its starting position by means of a spring force. The use of a spring for this purpose also has the advantage that the return stroke of the pressure plate will be less liable to injure the operator. The operator of the known wood splitters stands a serious risk of injury when the pressure plate is returned at such high hydraulic pressures as those concerned.
EP-A1-0 051 853 discloses a wood splitter of this general kind which, however, comprises a manually operated valve. In one embodiment of the wood splitter it is said that this valve could be replaced by an automatically operated valve so that the hydraulic fluid can be supplied to the piston-cylinder device through said valve which is controlled by the hydraulic pressure, such that feed movement of the pressure plate is initiated when the hydraulic pressure rises and that the pressure plate is returned to its starting position by a return spring, when the hydraulic pressure falls.
The valve proposed to be used in the above embodiment seems not to be able to fulfill the intended function as the discharge conduit will not open as there will be no substantial pressure difference between the opposite surfaces of the rim portion of the flexible membrane as the delivery flow of hydraulic oil is discontinued.